Field of the Invention
The present invention relates to an image processing apparatus and a method for processing an image.
Description of the Related Art
An inkjet recording apparatus is known that records an image by repeating a scanning operation in which ink is discharged while a recording head that includes a discharge port column including a plurality of discharge ports that discharge ink is being relatively moved over a unit area of a recording medium in a scanning direction and a sub-scanning operation in which the recording medium is conveyed in a conveying direction, which is perpendicular to the scanning direction. A so-called “multipass recording method” is also known in which such an inkjet recording apparatus forms an image by performing a plurality of scanning operations in a unit area.
It is known that, in an inkjet recording apparatus, discharge characteristics such as the amount of ink discharged and a discharge direction might vary between discharge ports. This can be because of various types of variation such as variation in the diameter of the discharge ports due to manufacturing errors and variation in the amount of heat generated by recording elements that generate thermal energy. If such variation in the discharge characteristics of the discharge ports occurs, color misregistration, in which colors are unintendedly misregistered, might occur in a recorded image. In Japanese Patent Laid-Open No. 2006-305954, test patterns are recorded on a recording medium and correction values for correcting discharge characteristics of discharge ports are obtained on the basis of the test patterns in order to correct original image data on the basis of the correction values. By recording an image in accordance with recording data generated using the corrected image data, color misregistration due to variation in the discharge characteristics can be suppressed.
If recording is performed using the multipass recording method, however, an image corresponding to a certain area of the recording medium is recorded by different discharge ports in a plurality of scanning operations. In view of this, in Japanese Patent Laid-Open No. 2011-025685, correction values for correcting image data corresponding to an image to be recorded in a certain area are calculated on the basis of correction values of a plurality of discharge ports obtained on the basis of test patterns and contribution ratios, which are ratios of contribution of the plurality of discharge ports to the recording in the certain area, of the plurality of discharge ports. The contribution ratios are calculated on the basis of recording permission ratios of mask patterns, which are used for distributing data among a plurality of scanning operations and in which recording permission pixels, in which recording is permitted, and recording inhibition pixels, in which recording is inhibited, are arranged. According to Japanese Patent Laid-Open No. 2011-025685, color misregistration due to variation in the discharge characteristics can be more effectively suppressed using the correction values calculated in the above-described manner.
If data is distributed differently depending on a plurality of partial areas obtained by dividing a unit area of a recording medium, the technique described in Japanese Patent Laid-Open No. 2011-025685 might not be able to perform effective correction. As a result, an image in which color misregistration is conspicuous might be recorded.